1. Field of the Invention
The application relates to a light-emitting element array. More particularly, the application relates to an organic electroluminescent (OEL) lighting element array.
2. Description of Related Art
An organic electroluminescent (OEL) element is an optoelectronic element capable of efficiently converting electric energy into light energy, and the OEL element often serves as an illumination source, a display panel, and so forth. Since the OEL element is characterized by the absence of viewing-angle dependence, simple manufacturing process, low costs, high response speed, wide operating temperature range, and full-color display, the OEL element satisfying the requirement for the multi-media display has become a popular research topic in recent years.
When the OEL element is applied in the field of illumination, the OEL element is often required to be capable of illuminating a large area. In order to provide a sufficient illumination area, manufacturers usually arrange a plurality of OEL lighting elements in arrays in series or in parallel, so as to form an OEL lighting element array. The anode of each of the OEL lighting elements is usually made of a transparent conductive material (e.g., indium tin oxide (ITO)) that often has a relatively high resistance. Nonetheless, when the illumination area is expanded, an issue of voltage drop (IR drop) in the OEL lighting element array often occurs, which leads to uneven brightness of the illuminative OEL lighting element array.
In order to resolve the issue of voltage drop, a metal mesh connected to the transparent anode may be used. However, the metal mesh does not allow light transmission, and thus the location where the metal mesh is disposed may become a dark zone that do not permit light passing through. Moreover, the refraction index of the transparent conductive material including ITO is greater than the refraction index of the substrate which carries the OEL lighting element, and light obliquely emitted from the anode to the substrate is likely to encounter total internal reflection (TIR) due to the difference in the refraction indexes of different materials. As such, the external quantum efficiency of the OEL lighting element array is not satisfactory.